A known power generating system for a cogeneration system is disclosed in JP2007-221916A (i.e., hereinafter referred to as Patent reference 1). The power generating system disclosed in the Patent reference 1 includes an engine driven by a combustion of a fuel, a generator actuated by the engine, a first converter converting an alternating current power generated by the generator into a direct current component, a second converter converting the direct current converted by the first converter into a alternating current power for a load (load alternating current power) and interconnected to a commercial power source as a system, and a control device controlling the first converter and the second converter. The first converter and the second converter construct an inverter device.
An alternating current of the load alternating current power outputted by the second converter of the inverter device occasionally includes a direct current component. In those circumstances, the direct current component may affect an operation of an alternating current power load connected to the inverter device. A guideline does not allow a direct current component to be included being equal to or greater than one percent (1%) of a rated current. The guideline requires to immediately disconnect (parallel off) the inverter device from the system when the alternating current of the load alternating current power outputted from the inverter device includes a direct current component equal to or greater than one percent. According to an inverter device for a small-sized cogeneration system, for example, in a case where 5 A of current is outputted when 1 kW of power is consumed, 50 mA is assumed to be a threshold value (i.e., corresponding to one percent of the rated current). In those circumstances, measurement that the alternating current of the load alternating current power includes the direct current component may be assumed to be extremely difficult. A direct current-current transformer (DC-CT) serving as an electric current sensor as an electric current detection means is moderately-priced as an electric current detection sensor. However, there is a drawback that, according to the DC-CT, a precision of measurements is likely to be affected by the temperature and a temperature drift is significant. For example, according to the DC-CT serving as the electric current sensor, there is a drawback that the temperature drift is generated because of the heat generation in use of the system, errors based on the temperature drift is added to detected values of the direct current component, and the direct current component included in the alternating current of the load alternating current power is not detected with high precision.
A need thus exists for a power generating system which is not susceptible to the drawback mentioned above.